Mark Taylor an international law expert and a director at the Fafo Institute for International Studies in Norway, told Al Jazeera the evidence so far "indicated that there's a case to be made that a war crime may have been committed".

"It's the American authorities, the US military that has to take a closer look at this investigation.

"There are questions about the way the investigation was conducted and whether or not it was done in a proper manner," he said.